Yellow leafs

Etheir Not enough nutrients like magnesium, or you had a blokus nutriment. Clean your soil and you back the right nutriment after drying

maybe not enough nutriens or a little sunburn?..

Check there poisition, are they old? If they very old they simply reached their limits and getting ready for there ever lasting sleep. Checked your diary, looks pretty normal to me, especially because rest of the plant is healthy